A simple approach to estimate gas permeability and selectivity of extremely thin and brittle materials

We have determined that the permeability and selectivity of ultrathin poly (4-vinyl pyridine) (PVP) material using the basic concept of microporous composite hollow fibers, pre-wetting technology and the resistance model. The calculated O₂ and N₂ permeabilities of an ultrathin PVP layer (~ 400 Å) at room temperature are about 0.40 and 0.049 Barrers, respectively, and the O₂/N₂ selectivity is approximately 8.3. To measure the permeability and selectivity of ultrathin brittle materials, two types of composite membranes have to be prepared; one is the silicone rubber/substrate membrane and the other is the silicone rubber/brittle material/substrate membrane prepared by the pre-wetting method. The substrate is preferred to be highly permeable with minimum surface defects. The pre-wetting agent is to prevent pore intrusion by sealing surface pores of the substrate before depositing the brittle material on the top of the substrate. Mathematically, the pre-wetting simplifies the resistance model to calculate the permeance of the ultrathin brittle material.